Composition and method for cleaning residual debris from semiconductor surfaces

ABSTRACT

A method for removing a dielectric anti-reflective coating (DARC) of silicon oxynitride material from a layer of insulative material which is formed over a substrate in a semiconductor device involves contacting the DARC material with a mixture of tetramethylammonium fluoride and at least one acid such as hydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acid or ethylenediamine tetraacetic acid. Contact with the mixture is for a time period sufficient to remove substantially all of the DARC material. The mixture has a high etch rate selectivity such that the DARC coating can be removed with minimal effect on the underlying insulative layer.

This application is a divisional of application Ser. No. 09/730,769,filed on Dec. 7, 2000 now U.S. Pat. No. 6,391,794, which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to cleaning residual contaminants fromsemiconductor devices, and more particularly, to a new composition andmethod for etch removal of undesirable materials from areas near contactopenings on wafer surfaces. The invention also relates to thesemiconductor structures cleaned in accordance with the formulation andmethod hereinafter described.

BACKGROUND OF THE INVENTION

In the formation of contact openings or vias in semiconductor devicesused to provide conductor-to-conductor contacts, it is often necessaryto etch through one or more layers of insulative material formed over asubstrate. FIG. 1 shows a cross section of a portion of a semiconductordevice 10 in an intermediate stage of fabrication. The device has asubstrate 12. The substrate is formed of a material such as silicon.Field oxide regions 13, transistor gate stacks 15, spacers 17 protectingthe gate stacks, and doped regions 19 are formed over the substrate. Thesubstrate 12 also has at least one conductive area in the form of aconductive “plug” 21, e.g. a polysilicon plug, formed thereover whichhas been deposited through a first layer of insulating material 23,which is usually a type of glass oxide available in the art, forexample, Boro-Phospho-Silicate Glass (BPSG), or silicon oxide materialsuch as silicon dioxide or Tetraethylorthosilicate (TEOS). The firstlayer of insulating material 23 may, in actuality, be formed as one ormore layers of insulating material of, for example, BPSG or TEOS. Theinsulating layer 23 may be anywhere from a few hundred Angstroms toseveral thousand Angstroms in thickness. The top of layer 23 and the topof plug 21 may also be substantially coplanarized using availablemethods.

As shown in FIG. 2, a second insulative layer 25 is formed over thefirst insulative layer 23. The second insulative layer 25 may becomprised of the same or different material than that of the firstinsulative layer 23, and can also comprise BPSG, for example. Adielectric anti-reflective coating (DARC) layer 27 is formed over thesecond insulative layer 25 using available methods. The DARC layer 27 istypically comprised of silicon oxynitride and may be a few Angstroms toseveral hundred Angstroms in thickness. A photoresist layer 29 ispatterned over the DARC layer 27 to provide access to the conductiveplug 21 as represented by the dotted lines in FIG. 2.

Referring now to FIG. 3, a contact opening 31 is formed through the DARClayer 27 and the second insulative layer 25. The contact opening 31 ispreferably formed using available etching methods, in particular dryetching using one or more available fluorinated hydrocarbons that areexposed to acceptable operating parameters. The etch stop is preferablythe top of the conductive plug 21. The DARC layer 27 prevents thephotoresist layer 29 from being exposed to light which is otherwisereflected off the insulative layer 25, which during the developing ofphotoresist layer 29 causes it to have an incorrect opening for etching.

As shown in FIG. 4, after formation of the contact opening 31 thephotoresist layer may be stripped using available methods. Removal ofthe photoresist layer leaves the exposed DARC layer 27 over the secondinsulative layer 25 which must also be removed. The DARC layer 27,comprised of silicon oxynitride, and although a solid dielectric layerit has a tendency to leak at times, and may therefore interfere withsubsequent metallization of the contact opening 31, e.g. metallizationduring capacitor formation. Its removal is therefore highly desirable.At the same, it is also desirable to remove this layer with minimaleffect on the second insulating layer 25, e.g. with minimal or noremoval of layer 25.

To date, removal of the DARC layer 27 has been achieved using chemicalformulations that have included such compounds as ammonia fluoride(NH₄F) mixed with phosphoric acid (H₃PO₄). One reference, U.S. Pat. No.5,981,401 to Torek et al. describes a method for selective etching ofantireflective coatings. However, this document only discloses etchratios that are greater than 1 or 2. This would indicate that theunderlying insulative layer is still being etched at a rather high raterelative to the di-electric anti-reflective coating layer. In addition,the patentees recommend etchant solutions with very high (basic) pH's toachieve etch rates greater than 1. They disclose pH's which exceed 11,and desirably are between 11 and 14.

Unfortunately, none of the compositions or methods available in the arthave been totally satisfactory in removing the DARC layer, whileminimally affecting the underlying insulative layer. Some have been tooweakly formulated so that the DARC layer is not adequately removed;others have been too strong or corrosive such that a significant portionof the insulative material is removed as well.

Thus, there exists a need in the art for an improved formulation andmethod for removing dielectric anti-reflective coating (DARC) layers, aswell as other residual debris that may be formed during other stages ofsemiconductor fabrication, such as during formation of contact openings.

SUMMARY OF THE INVENTION

In accordance with the invention, there is set forth a method ofremoving a dielectric anti-reflective coating comprising contacting thecoating with a removal mixture containing tetramethylammonium fluorideand at least one acid selected from the group consisting of hydrofluoricacid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid,citric acid, sulfuric acid, carbonic acid and ethylenediaminetetraacetic acid.

In a further embodiment of the invention a composition suitable for usein removing a silicon oxynitride dielectric anti-reflective coating isprovided. The composition comprises about 10 to about 40% oftetramethylammonium fluoride; and about 0.15 to about 6% of at least oneacid selected from the group consisting of hydrofluoric acid,hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citricacid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid.The composition may also contain from about 1 to about 15% of anoxidizing agent such hydrogen peroxide, ozone, or ammonium persulfate.

The invention also provides a method of removing silicon oxynitridematerial by contacting it with a mixture of tetramethylammonium fluorideand at least one acid selected from the group consisting of hydrofluoricacid, hydrochloric acid, nitric acid, phosphoric acid, acetic acid,citric acid, sulfuric acid, carbonic acid and ethylenediaminetetraacetic acid. The contacting is performed at a temperature withinthe range of about 10 degrees C. to about 70 degrees C.

Further provided as part of the invention is a method of forming acontact opening in an insulative layer formed over a substrate in asemiconductor device. The method comprises forming a dielectricantireflective coating layer over the insulative layer, and then forminga photoresist layer over the coating layer. The photoresist layer ispatterned and exposed to provide an etch mask. A contact opening is thenetched through the insulative layer using the etch mask. The photoresistlayer is then removed, and the coating layer is contacted with a removalmixture containing tetramethylammonium fluoride and at least one acidselected from the group consisting of hydrofluoric acid, hydrochloricacid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuricacid, carbonic acid and ethylenediamine tetraacetic acid, with thecontacting being sufficient to remove the coating layer.

In addition, the invention provides a method of chemical mechanicalplanarization. A top portion of a conductive plug is planarized with atop portion of an insulative layer formed over a substrate in asemiconductor device. At least one of the top portions is then contactedwith a mixture of tetramethylammonium fluoride and at least one acidselected from the group consisting of hydrofluoric acid, hydrochloricacid, nitric acid, phosphoric acid, acetic acid, citric acid, sulfuricacid, carbonic acid and ethylenediamine tetraacetic acid.

The invention further provides a semiconductor device having asubstrate, and a contact opening formed in an insulative layer over thesubstrate, wherein at least the contact opening or the portion of theinsulative layer around the contact opening, and preferably bothregions, have been cleaned with a mixture of tetramethylammoniumfluoride and at least one acid selected from the group consisting ofhydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid,acetic acid, citric acid, sulfuric acid, carbonic acid andethylenediamine tetraacetic acid.

Additional advantages and features of the present invention will becomemore readily apparent from the following detailed description anddrawings which illustrate various exemplary embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a semiconductive wafer device in anintermediate stage of fabrication according to a first embodiment of theinvention.

FIG. 2 is the device shown in FIG. 1 in a further stage of fabrication.

FIG. 3 is the device shown in FIG. 2 in a further stage of fabrication.

FIG. 4 is the device shown in FIG. 3 in a further stage of fabrication.

FIG. 5 is the device shown in FIG. 4 utilizing the composition andmethod of the invention to remove a DARC layer.

FIG. 5A is the device shown in FIG. 5 after the DARC layer has beenremoved.

FIG. 6 is another cross section of a semiconductive wafer device in anintermediate stage of fabrication according to another embodiment of theinvention

FIG. 7 is the device shown in FIG. 6 in a further stage of fabrication.

FIG. 8 is the device shown in FIG. 7 in a further stage of fabrication.

FIG. 9 is another cross section of a semiconductor wafer device in anintermediate stage of fabrication according to another embodiment of theinvention.

FIG. 10 is another cross section of a semiconductor wafer device in anintermediate stage of fabrication according to another embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment, the invention relates to a method of removing adielectric anti-reflective coating from an insulative layer.

Reference herein shall be made to the terms “substrate” and “wafer”,which are to be understood as including silicon, a silicon-on-insulator(SOI) or silicon-on-sapphire (SOS) structures, doped and undopedsemiconductives, epitaxial layers of silicon supported by a basesemiconductive foundation, and other semiconductive structures. Inaddition, when reference is made to a “substrate” or “wafer” in thefollowing description, previous process steps may have been utilized toform arrays, regions or junctions in or over the base semiconductivestructure or foundation. In addition, the semiconductive material neednot be silicon-based, but could be based on silicon-germanium,germanium, indium phosphide, or gallium arsenide. The term “substrate”as used herein may also refer to any type of generic base or foundationstructure.

Referring again to the drawings with reference now to FIG. 5, after theetching of the insulative layer 25 illustrated in FIG. 4, the DARC layer27 is contacted with a mixture of tetramethylammonium fluoride (CH₃)₄NF(TMAF) and at least one acid selected from the group consisting ofhydrofluoric acid, hydrochloric acid, nitric acid, phosphoric acid,acetic acid, citric acid, sulfuric acid, carbonic acid andethylenediamine tetraacetic acid (EDTA). This mixture of TMAF and acidmay be referred to herein as a removal mixture. Preferably, the removalmixture comprises about 10 to about 40% of TMAF, and more preferablycontains about 20 to about 25% thereof. Even more desirably, the mixturewill contain about 21 to about 24% of tetramethylammonium fluoride(unless otherwise stated, all percentages herein are weightpercentages). Besides TMAF, other compounds with the formula R₄NF may beutilized in the removal mixture, where R is a straight or branched chainC₁-C₂₀ alkyl group. (When TMAF is utilized, it may be obtained as astock solution containing about 25 wt % of TMAF; however, otherformulations are also within the scope of the invention.)

The acid will be present in the removal mixture in amounts of from about0.15 to about 5%, with amounts within the range of about 0.3 to about 1%being more preferred. Especially preferred is an amount of acid in theremoval mixture within the range of about 0.5 to about 1%. The remainderof the removal mixture is typically water in a quantity sufficient toobtain 100 total weight percent.

Preferably, the acid is at least one member selected from the groupconsisting of hydrofluoric, phosphoric and acetic acids. Of these,hydrofluoric acid is particularly desirable. Thus, a removal mixturecomprising tetramethylammonium fluoride (TMAF) and hydrofluoric acid isparticularly preferred. When hydrofluoric acid is utilized, it isusually obtained as a 49 wt. % solution; however, other suitable andgenerally available concentrations are also within the scope of theinvention. Other desirable formulations include TMAF with phosphoricacid, as well as TMAF with acetic acid. Especially preferred,non-limiting formulations include TMAF (about 20-25%, more preferablyabout 23%) with about 0.5 to about 1.0% of hydrofluoric acid; TMAF(about 20-25%, more preferably about 23%) with about 2 to about 4% ofphosphoric acid; and TMAF (about 20-25%, more preferably about 23%) withabout 5 to about 10%, preferably about 7% of acetic acid.

In a further embodiment of the invention, the tetramethylammoniumfluoride (TMAF) may be generated from a reaction mixture oftetramethylammonium hydroxide (TMAH) and hydrofluoric acid (HF)according to the following reaction scheme:

(CH₃)₄NOH+HF→(CH₃)₄NF+H₂O

The TMAF is then further admixed with one or more of the acids set forthabove. If the acid selected is hydrofluoric acid, then it may be addedin a stoichiometric excess to that necessary to generate the TMAF in thereaction scheme set forth above.

In a further embodiment of the invention, an oxidizing agent may beadded to the removal mixture of TMAF and acid(s) described above.Preferably, the oxidizing agent is chosen to form an oxidizing etchantwith the removal mixture so as to enhance etch rate selectivity. Asuitable oxidizing agent may be one or more members selected from thegroup consisting of hydrogen peroxide (H₂O₂), ozone (O₃), ammoniumpersulfate and nitric acid. Of these, hydrogen peroxide may be preferredin many applications. When added, the oxidizing agent will compriseabout 1 to about 15% of the etchant removal mixture. More preferably,the oxidizing agent will make up about 3 to about 10% thereof. Anespecially preferred, non-limiting etchant removal mixture willtherefore comprise about 20 to about 25%, more preferably about 23% ofTMAF; about 2 to about 4% of phosphoric acid; and about 1 to about 10%,preferably about 3% of hydrogen peroxide.

In a preferred embodiment of the invention, the combination of TMAF andacid chosen (plus any additional components, e.g. oxidizing agent(s)) issuch that an etch rate selectivity ratio of at least about 5:1, and morepreferably at least about 10:1 is obtained. Especially preferred is anetch rate selectivity ratio of at least about 15:1. As that term is usedherein, “etch rate selectivity ratio” means the rate at which the DARClayer 27 is etched relative to the rate at which the insulatingmaterial, e.g. BPSG or TEOS comprising the underlying insulative layer25, is etched (etch rate being typically measured in Angstroms/minute).For an etch rate selectivity of about 5:1, this means that the removalmixture will etch the DARC layer 27 about 5 times faster than theunderlying insulative layer 25. Thus, the combination of TMAF andacid(s) chosen should maximize removal of the DARC layer 27, whileminimally abrading the underlying insulative layer 25. Conversely, it isparticularly preferred that the combination of TMAF and acid chosen besuch that TMAF's utility at reducing the etch rate of the insulativelayer, e.g. BPSG or TEOS, be maximized, while at the same timemaintaining the relatively high ionic strength of the fluoride ionuseful in removing silicon oxynitride polymers and other residualdebris.

In another embodiment of the invention, the removal mixture may have apH within the range of about 4 to about 14, and desirably may have asubstantially neutral pH which is within the range of about 6.5 to about8.5. More preferably, the pH of the solution is within the range ofabout 7 to about 8, and is more preferably about 7. Etch rateselectivities as described above can still be obtained within these pHranges, with the additional advantage being that the removal mixture isnot overly caustic or corrosive.

The removal mixture according to its various embodiments should bestorage stable for at least about 24 hours, and more preferably for atleast about 1 week. As that term is used herein, “storage stable” meansthat the removal mixture should retain at least about 90% potency afterstorage at 25 degrees C. and about 1 atmosphere pressure for the statedperiods.

Removal of the DARC layer 27 can be usually be accomplished attemperatures within the range of about 10 to about 70 degrees Celsius,with about 20 to about 60 degrees being more preferred, and withtemperatures of about 20 to about 40 degrees being even more desirable.It has now been found that as a general rule, the higher the operatingtemperature, the faster the rate of DARC layer removal, but the lowerthe etch rate selectivity ratio.

Removal is preferably accomplished by dipping the portion of thesemiconductor device containing the DARC layer 27 in a bath containingthe removal mixture of TMAF and acid(s) described above. The contactingis performed for a time sufficient to remove at least most of, andpreferably substantially all of the DARC layer 27. The time forcontacting the DARC layer 27 with the TMAF/acid mixture will vary,depending upon such factors as the thickness of the layer and the etchrate selectivity. In most instances, however, the time period forcontacting will usually be within the range of about a few minutes toabout several minutes. Thus, the time period will typically be about 3minutes to about 15 minutes, with about 4 to about 6 minutes beingpreferred.

FIG. 5A illustrates the portion of the semiconductor device 10 in whichthe DARC layer 27 has been removed using the composition and method ofthe invention. Both the layer 27 and the opening 31 are shown clear ofresidual debris.

Referring now to FIGS. 6 and 7, there is shown a further embodiment ofthe invention on another portion of the semiconductor device 10 shown inFIG. 1. Another contact opening 41 may be formed in the insulative layer23 using available methods, including utilization of a DARC layer 27 anda photoresist layer 29 as heretofore described with reference to FIGS. 1through 4. Subsequent to removal of both the DARC layer and thephotoresist layer using available methods and following formation of adoped region 19 using applied chemical vapor deposition (CVD)techniques, for example, the inside of the opening 41 may be contactedwith titanium so as to form a thin conductive coating 43 thereover. Athin layer 44 of titanium nitride may also be formed or deposited at thebottom of the contact opening 41 over the doped region 19 of thesubstrate 12.

Referring to FIGS. 7 and 8, a tungsten plug 45 may then be formed in thecontact opening 41. The conductive coating of titanium 43 helps the plug45 to better adhere within the insulative layer 23, and when annealedwith nitrogen during a rapid thermal process, actually forms twoconductive material layers of titanium nitride and titanium silicide.The titanium silicide layer reduces the plug resistance, and togetherwith the titanium nitride layer (shown as component 44) helps to preventions from penetrating into the substrate during plug formation.Thereafter, the top of the plug 45 and the insulative layer 23 may becoplanarized using techniques such as chemical mechanical planarization,or CMP.

In theory, planarization should remove any residual titanium and/ortitanium nitride which may have built up over the insulative layer 23around the opening 41, as well as any residual DARC layer materialremaining thereover as well. In practice, however, residual contaminantsat the corner regions 47 illustrated in FIG. 7 remain, which caninterfere with the subsequent formation of a conductive metal runner 49over the plug 45 (as shown in FIG. 8). These residual contaminants canalso interfere with the electrical connection between the runner 49 andthe plug 45. Thus, the composition and method of the invention asheretofore described can be useful in removing residualtitanium/titanium nitride and DARC material (silicon oxynitrides) fromthe region 47 around the opening 41. Preferably this is accomplished bydipping as heretofore described, after planarization of the plug 45 withthe top of layer 23 and before formation of the conductive metal runner49.

EXAMPLE

The following example illustrates various embodiments of the invention,but should not be construed as limiting the scope thereof. In thisexample, etch rates (Angstroms/minute) for various formulations of theinvention were compared on BPSG, TEOS and DARC layers. The results areshown in TABLE 1:

Formulation BPSG TEOS DARC 23% TMAF, 0.5% HF 11.9 29.0 164.0 (21.5° C.)23% TMAF, 1.0% HF 19.3 47.9 228.2 (21.5° C.) 23% TMAF, 4% 19.9 54.0 1 KÅclear in 3 minutes H₃PO₄ (23° C.) 23% TMAF, H₃PO₄, 24.3 728 1 KÅ clearin 2 minutes 3% H₂O₂ (23° C.) 23% TMAF, 7% acetic 59.3 164.0 1 KÅ clearin 1 minute acid (36.8° C.) Same as above (27.9° C.) 32.0 82.9 1 KÅclear in 2 minutes Same as above (25° C.) 248 66.7 1 KÅ clear in 2.5-3minutes Same as above (21.5° C.) 20.0 50.9 254

As is shown in TABLE 1, the formulation according to various embodimentsof the invention exhibits high etch rate selectivity ratios for the DARClayer relative to an insulative layer comprised of either BPSG or TEOS.

A further application of the method and composition of the invention isillustrated with respect to FIG. 9. A semiconductor device 110 in anintermediate stage of fabrication has a base or substrate 112 which ispreferably comprised of a conductive material such as one or moremetals, and even more preferably is formed of copper. A dielectric orinsulative layer 114 has been formed over the substrate 112 usingavailable methods and may be comprised of a material such as BPSG orTEOS, for example. A trench or via 116 has also been formed in thedielectric layer 114. The shape of the trench or via 116 in FIG. 9 isshown for purposes of illustration only, and is not to be construed aslimiting. Trench or via 116 is formed using methods such as dry etchingwith available etch compounds. Metallic debris 118 is sputtered orotherwise deposited on the sides of the trench or via 116 as a result ofthe etch materials contacting the substrate 112. Use of the removalmixture of the invention according to the various embodiments asheretofore described will effectively remove the debris 118 while notcorroding either the dielectric layer 114 or the substrate 112.

Another application of the invention is shown with respect to FIG. 10. Asemiconductor device 210 in an intermediate stage of fabrication has anopening 216 formed in an insulative layer 214 which in turn has beenformed over a substrate 212. The substrate is comprised of silicon, orsilicon-on-insulator material as previously described with reference toFIG. 1. A layer of native oxide 218 has been deposited in the opening216 over the substrate 212 using available materials and techniques.Subsequent removal of the native oxide layer 218 is desirable as part ofa pre-diffusion cleaning step. In this process, the native oxide layer218 is removed from the substrate so that dopants may then be diffusedinto the substrate to form an active, doped region as illustrated by theline 220. Use of the removal mixture of the invention as heretoforedescribed will effectively remove the native oxide 118 while notcorroding either the insulative layer 214 or the substrate 212.

The foregoing description is illustrative of exemplary embodiments whichachieve the objects, features and advantages of the present invention.It should be apparent that many changes, modifications, substitutionsmay be made to the described embodiments without departing from thespirit or scope of the invention. The invention is not to be consideredas limited by the foregoing description or embodiments, but is onlylimited by the scope of the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A semiconductor device, comprising: asubstrate; and a contact opening formed in an insulative layer over saidsubstrate, wherein at least one of said contact opening and a portion ofthe insulative layer around said contact opening has been cleaned with amixture of tetramethylammonium fluoride, an oxidizing agent and at leastone acid selected from the group consisting of hydrofluroic acid,hydrochloric acid, nitric acid, phosphoric acid, acetic acid, citricacid, sulfuric acid, carbonic acid and ethylenediamine tetraacetic acid.2. The device of claim 1, wherein said device has a conductive plugformed in said contact opening after said cleaning.
 3. The semiconductordevice of claim 1 wherein said oxidizing agent is present in an amountof from about 1 to about 15%.
 4. A composition suitable for use inremoving a silicon oxynitride dielectric anti-reflective coating,comprising: about 10 to about 40% of tetramethylammonium fluoride; andabout 0.15 to about 6% of at least one acid selected from the groupconsisting of hydrofluoric acid, hydrochloric acid, nitric acid,phosphoric acid, acetic acid, citric acid, sulfuric acid, carbonic acidand ethylenediamine tetraacetic acid.
 5. The composition of claim 4,wherein said composition comprises about 20 to about 25% oftetramethylammonium fluoride.
 6. The composition of claim 4, whereinsaid acid is selected from the group consisting of hydrofluoric acid,nitric acid and phosphoric acid.
 7. The composition of claim 6, whereinsaid acid comprises about 0.3 to about 1% of said composition.
 8. Thecomposition of claim 7, wherein said acid comprises about 0.5 to about1% of said composition.
 9. The composition of claim 4, furthercomprising at least one oxidizing agent.
 10. The composition of claim 9,wherein said oxidizing agent is at least one member selected from thegroup consisting of hydrogen peroxide (H₂O₂), ozone (O₃), ammoniumpersulfate and nitric acid.
 11. The composition of claim 10, whereinsaid oxidizing agent is hydrogen peroxide.
 12. The composition of claim9, wherein said oxidizing agent comprises about 1 to about 15% of saidcomposition.
 13. The composition of claim 4, wherein said compositionhas an etch rate selectivity ratio of at least about 5:1.
 14. Thecomposition of claim 13, wherein said composition has an etch rateselectivity ratio of at least about 10:1.
 15. The composition of claim4, wherein said composition is storage stable for at least about 24hours.
 16. The composition of claim 4, wherein said composition isstorage stable for at least about one week.
 17. The composition of claim4, wherein said composition has a substantially neutral pH.
 18. Thecomposition of claim 17, wherein said composition has a pH within therange of about 7 to about 8.